Ischemic brain damage is a major factor contributing to high rates of both disability and mortality following heart failure. Cardiac arrest leads to selective cell death in both hippocampus and cortex, as well as vascular leakage and edema. Oxidative stress is a major feature of ischemic brain damage, and 12/15-lipoxygenase (12/15-LOX) is one of its main mediators. In this proposal, we plan to investigate the contributions of 12/15- LOX to both vascular damage and neuronal cell death following global ischemia induced by cardiac arrest. We have previously established 12/15-LOX as a major contributor to delayed neuronal cell death and leakage of the blood - brain barrier following transient focal ischemia. In addition, we have elucidated a major cell death pathway centered on 12/15-LOX. Here, we will use mouse models of cardiac arrest and global cerebral ischemia to investigate increased 12/15-LOX expression after cardiac arrest. Our central hypothesis states that increased vascular and neuronal 12/15-LOX exacerbates brain damage by causing oxidative stress, leading to vascular leakage, edema, and the death of neurons. Our preliminary results show that a) expression of 12/15-LOX is increased in a mouse model of cardiac arrest and resuscitation; b) 12/15-LOX co-localizes with MDA2, a marker for oxidative stress, as well as FluoroJade B, a marker for cellular injury; c) these findings can be replicated in a model of global cerebral ischemia; and d) mice in which 12/15-LOX has been genetically deleted show reduced damage after cardiac arrest. We propose to study the consequences of 12/15-LOX up-regulation in mouse models of global ischemia in the following specific aims. In Aim 1, we characterize the expression of 12/15-LOX in a mouse model of cardiac arrest with resuscitation. Besides determining the cell types expressing 12/15-LOX, we will investigate markers of oxidative stress and cellular damage. In addition, we will measure levels of edema and vascular leakage. In Aim 2, we study the protection through 12/15-LOX gene knockout against neural cell death and edema formation in the mouse model of cardiac arrest and resuscitation. In Aim 3, we investigate the protective potential of pharmacologically inhibiting 12/15-LOX with a specific inhibitor, and compare with therapeutic hypothermia treatment. We will determine both short- and long-term outcome, using behavioral tests and histological measures. Severe ischemia and reperfusion injury is associated with cardiac arrest and subsequent cardiopulmonary resuscitation. Elucidating the role of 12/15-LOX in mediating ischemic damage may lead to novel therapeutic options in treating cardiac arrest patients.